Monomer and dimer emissions in the solutions of a monosubstituted polyacetylene

Photoluminescence (PL) of tetrahydrofuran solutions of a monosubstituted po lyacetylene with liquid crystalline pendants, poly(11-{[4'-heptoxy-4-biphen ylyl)carbonyl]oxy}-1-undecyne) (1), has been investigated. Intense ultravio let emission (similar to 370 mn) has been detected in its dilute solution ( 2.5 muM). As the solution becomes concentrated (up to 39 mM), the emission color changes to deep blue and finally to blue ( similar to 430 nm). In add ition to the large-scale red shift in PL peak, its luminescent intensity ch anges about two orders of magnitude. Based on the extended Huckel tight-bin ding calculations, the 370 nm peak is assigned to monomer emission, which o riginates from the biphenyl mesogen in the pendants, and the peak at 430 nm corresponds to dimer emission, which is related to the aggregates formed i n concentrated solutions. Lyotropic mesophase was observed as I dissolves i n tetrahydrofuran. (C) 2001 Elsevier Science B.V. All rights reserved.